This invention relates generally to large character, dot matrix, drop-on-demand printers used, for example, to print shipping addresses on the side of cartons at a warehouse, and in particular, the invention relates to a novel printing head used in such a drop-on-demand printer.
Large character, dot matrix, drop-on-demand printer systems are growing in popularity for industrial and warehouse operations to print shipping information and inventory control data on the sides of cardboard and plywood cartons containing particular goods. Such printers print characters from 3/8" to as much as 3" in height using such as a 5.times.7 dot matrix character format to perform the printing as the carton is moved past the upstanding printing head nozzles. The 5.times.7 matrix is effected by 7 linearly arranged nozzles being used to print dots at each of 5 steps transverse of the nozzle line as the carton is moved therepast. Additional nozzles can be used to print two or more lines of copy, print larger sizes characters and enhance the readability of the resultant character. Four printing heads can be used for the usual four lines of addresses, and eight heads can be used to print on opposite sides of the cartons.
Users of the drop-on-demand printers regularly change the dot matrix spacing to conform the character size to their changing applications. Manufacturers of the drop-on-demand printers satisfy this need by supplying nozzle arrays of different spacing; the means for connecting the variously spaced nozzle arrays to the valving assembly being thin, flexible tubing. This tubing interconnection has one benefit, but has several drawbacks. The tubing is beneficial to aid in disconnecting a nozzle that is clogged and that can be cleared by vacuum or pressure applied directly to the nozzle to flush the nozzle clean.
The tubing connection arrangement is cumbersome, however. In changing to another nozzle array all seven or more (typically up to 16) closely bunched tubes must be removed from the one array and reconnected in the correct order to the new array. This is in addition to removing and replacing the nozzle array fasteners and is while the hanging tubing is dribbling ink. Of course, the shipping line is inactive during the changeover operation.
A more serious shortcoming occurs when a dot stops being printed; the cause can be either a manfunctioning valve or a clogged nozzle. Usually the operator stops the printing line and its attendant production while he searches for the cause and corrects it. The operator can interchange two of the ink supply tubes to determine whether the cause is the valve or nozzle but he later must remember to reconnect the tubes correctly. If the problem is the nozzle, he can flush it out, while the associated tube is hanging and dribbling ink, re-connect the tube, close the print head and continue printing. Clearing a clogged nozzle can be complicated by additional printing heads above and below the head or array comprising the offending nozzle. Heads or arrays customarily are arranged closely spaced on their mounting frame according to the desired location of the printing line on the container. Thus, clearing a clogged nozzle is tedious at best and the loss of printing and attendant production time is costly.